Lattice effects on the multiferroic characteristics of (La, Ho) co-substituted BiFeO3

Abstract The influence of La3+ and Ho3+ co-substitution on the structural, electrical and magnetic properties of rhombohedrally distorted polycrystalline BiFeO3 is reported. The presence of a tiny residual secondary phase of Bi2Fe4O9, Bi25FeO40 is evident in all the samples, while La doping suppresses the impurity phase and favours the grain growth (size of 1-2 μm) of the pristine compound. A fivefold increase in the dielectric constant (230 at 1 MHz) is achieved for the samples with the highest La content with a remarkable reduction in the dielectric loss. LaxHoyBi1-(x+y)FeO3 ceramics exhibit lossy ferroelectric loops and the magnitude of polarization reduces upon the co-substitution. The antiferromagnetic BiFeO3 transforms to ferromagnetic at low temperatures due to the annihilation of the cycloid-spin structure. The co-substitution effectively improved the magnetic properties. ‘Ho’ substitution helps in achieving the enhanced magnetization values while ‘La’ substitution helps in increasing the magnetic coercivity, HC. The variation of the HC with the temperature is interpreted by means of the two sublattice model.